Thermoplastic elastomer composites for stiff core golf balls and method for making same

ABSTRACT

A golf ball is provided that includes at least one layer of material that is a composite of thermoplastic and a second phase material that is dispersed within the thermoplastic. This material may be a blend of thermoplastic and elastomeric material. Preferably, the golf ball comprises a hard sphere core such as a hollow metal core, a layer of Thermoplastic Elastomer Composite, and a cover layer. This results in a golf ball that is legal for play and capable of drive distances essentially equivalent to those of currently available high performance golf balls, but also provides a ball that has less hook and slice during play, while being durable and economical to produce.

FIELD OF THE INVENTION

The present invention relates generally to an improved multi-piece golfball, and more particularly, a multi-piece golf ball including a hardspherical core or layer with improved characteristics. Moreparticularly, the present invention relates to an improved golf ballhaving a blend of an injection moldable polymer and non-injectionmoldable polymer, in one or more layers of a golf ball.

BACKGROUND OF THE INVENTION

Most golf balls sold in the U.S. are listed on the conforming list ofthe United States Golf Association—the USGA. Several specifications havebeen established by the USGA, and a golf ball must meet certain testcriteria relating to these specifications for weight, size, initialvelocity, overall distance (carry and roll), and spherical symmetry. Foracceptance by the USGA a golf ball must not weigh more than 1.620ounces, must have a minimum diameter of 1.680 inches, must have amaximum initial ball velocity of 250 feet per second (plus a maximum 2%tolerance) as measured on a standard USGA ball testing machine, musthave an overall distance maximum of 317 yards (plus a maximum 3 yardtolerance) as measured by the USGA overall distance test procedure.Further, the ball must not be designed, manufactured or intentionallymodified to have properties that differ from those of a sphericallysymmetric ball. The USGA tests for symmetry by inspecting thestatistical deviation of the overall distance test data (distancevariation and flight time variation) when the ball is struck fromvarious aspects.

In the modern era of golf, a typical golf ball has been either of the‘wound’ or ‘molded’ type. Since molded golf balls are cheaper toproduce, virtually all of the golf balls currently sold today aremolded. The major manufacturers have ceased production of wound balls inpursuit of more sophisticated molded type balls. Due to their low price,most golf balls sold today are two-piece polymeric balls withpolybutadiene cores and ionomer covers. The process of making this typeof ball includes first compression molding the polybutadiene into asolid core and then injection molding a cover onto this core. Dimplesare included in the die and so the second step of injection moldingproduces a nearly finished golf ball—clean up and painting is typicallyperformed to finish the ball. Most development of new golf balls isbased on the simple two-piece architecture—employing the solidpolybutadiene core, but adding various layers between this core and theoutermost cover. First, a two-layer cover appeared, then multiple layerswith as many as five or six total layers. Also, new materials have beenemployed for the various covers. Some balls use an injection molded coreor mantle layer (between the core and cover layers) but the majority ofeven the best selling tour balls employs the proven compression moldedpolybutadiene core.

One common factor amongst the far majority of golf balls today is thematerials of construction. Most commercially available golf balls aremade of nonmetallic rubbers and plastics, such as elastomers, ionomers,polyurethanes, polyisoprenes, nylons, and other similar materials. Inrecent years, however, golf balls incorporating metals have appeared inthe market. For example, U.S. Pat. Nos. 6,004,225, 6,705,957, and6,976,925 disclose a golf ball having a hollow metal core. This designtakes advantage of the high stiffness of the metal core (when comparedto the stiffness of typical golf ball materials) to achieve a golf ballthat has simultaneous characteristics of high accuracy (less hook andslice) as well as excellent putting characteristics. These types of golfballs may have a couple of shortcomings, including hard feel and a smallloss of distance compared to more typical molded balls discussed above.Accordingly, there is a need for golf balls that have a hollow metalcore that do not exhibit some or all of the shortcomings of these golfballs appearing in the art. Furthermore, there is a need for materialsthat allow a golf ball designer to control the stiffness of the core,while also avoiding the shortcomings observed in high stiffness cores.Perhaps most importantly, needs should be met in a manner that allows aneconomical means of production.

Simply using a metal in part of the golf ball is not sufficint tosignificantly increase the stiffness of the golf ball. A few very oldpatents discuss a ball having a hollow metal sphere of some type. SeeU.S. Pat. Nos. 697,816; 700,658; 713,772; 1,568,513; and 1,568,514, eachof which is hereby incorporated herein by reference. However, theseprior art designs suffer from several shortcomings including a hollowmetal sphere design that is not durable enough to withstand impactforces from being struck by a club. For example the '514 patent providesa golf ball having a hollow metal sphere comprising half shells. Thehalf shells are only 0.005 inches in thickness with scalloped edges thatare fit together but not securely joined. These patents do not disclosea golf ball design having a hollow metal sphere that can withstand theimpact of a golf club without permanent distortion or an efficient orcost effective method of manufacturing the golf balls. Not surprisingly,the golf balls are not believed to have achieved any commercial success.

Other designs have looked at new materials, but have either notattempted or accomplished a design that provides a significantly higherstiffness in the core (i.e., stiffness greater than 5× that of a typicalpolybutadiene core.) For example, U.S. Pat. No. 6,710,114, which ishereby incorporated herein by reference, provides golf balls having aportion or layer formed from a polymeric composite that includes atleast two polymers with distinct microstructures. The polymer compositemay include one or more reinforcing agents, such as nanoparticles thatare silica-based or carbon-based. According to the '114 patent,increasing the amount of nanoparticles can decrease the amount ofcrosslinking agent required to provide increased resilience but does notcreate a core with significantly higher stiffness.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball with a high stiffness core which is durable and capable ofmaintaining structural integrity and symmetry and which has good feel,rebound and flight trajectory.

Another objective of the present invention is the manufacture of ahollow metal core golf ball with materials that are compatible forenergy transfer between each layer without structural degradation ofeither material.

These and other objects are provided, according to the presentinvention, by a golf ball which includes a hollow metal sphere orcomposite sphere as the core and one or more outer layers surroundingthe sphere comprising a durable blended polymer that can withstand theextreme forces when compressed between a golf club and hollow metalsphere encountered during play. The blended polymer is comprised of ablend of at least two components, wherein one of the components is aninjection moldable polymer. A hollow metal sphere may be comprised of asteel, steel alloy, a nanostructured steel material, titanium andtitanium alloys. A composite core may include silicon nitride, carbonfiber, carbon nanotubes, graphene, and other high stiffness materials.

In one preferred embodiment of the present invention, a hollow metalsphere core is made of a 301 stainless steel alloy and is surrounded bya blended polymer layer, such as a mixture of ethylene (meth)acrylicacid ionomers (such as DuPont's HPF™ resin) and polybutadiene, which issurrounded by an ionomer cover that includes a dimple pattern. Betweenabout 1% and 80% and preferably between about 10% and 60% by weight ofthe polymer blend is polybutadiene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of the presentinvention golf ball including three material layers: (1) an innermostcore comprised of a hollow metal sphere, (2) a middle mantle layercomprised of Thermoplastic Elastomer Composite, and (3) cover layer.

FIG. 2 is a cross-sectional view of one embodiment of the presentinvention golf ball including three material layers: (1) an innermostcore comprised of solid core, (2) a middle mantle layer comprised ofThermoplastic Elastomer Composite, and (3) cover layer.

FIG. 3 is a cross-sectional view of one embodiment of the presentinvention golf ball including two material layers: (1) an innermost corecomprised of a hollow metal sphere or solid/porous composite sphere, and(2) a thick cover layer comprised of Thermoplastic Elastomer Composite.

FIG. 4 is a cross-sectional view of one embodiment of the presentinvention golf ball including one material layer: (1) a single layercomprised of Thermoplastic Elastomer Composite.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention is shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

U.S. Pat. Nos. 6,004,225, 6,705,957, and 6,976,925 each of which ishereby incorporated herein by reference, discuss a modern golf ball witha one-piece hollow metal sphere surrounded by a cover or a mantle layerand cover. The '225, '957, and '925 patents also discuss several methodsfor making the golf ball having a hollow metal sphere by hot forming orcold forming two halves of a sphere, which are securely joined togetherby various welding techniques or other sufficient means. This golf balldesign exhibits less hook and slice when miss hit. The one-piece hollowmetal sphere, which is surrounded by at least one polymer layer, iscapable of withstanding the hardest impacts from current titanium-facedgolf clubs. The '225, '957, and '925 patents disclose at least one layermade of polymers typically used in golf balls between the hollow metalsphere and the cover. Due to the presence of the high stiffness hollowmetal sphere, the polymer layer and cover are subject to a different setof stresses when compared to a conventional ball when struck by a club,which results in the unique flight characteristics.

During a high-speed collision between a golf ball and club, a golf ballundergoes deformation such that the core of the ball deforms from aspherical shape to an oblong shape. At the point of maximum deflectionof the golf ball, the ball and the club head travel together for amoment of time at the same velocity. After this point, the ball projectsforward, accelerating off of the face of the club due to the elasticnature of a golf ball. Based on the Coefficient of Restitution (COR) ofthe golf ball and the relative weight of the club head to that of thegolf ball, the golf ball travels at a faster speed than the club head.The initial velocity of the golf ball can be approximated with thefollowing equation:

$\begin{matrix}{v = {U \times \frac{1 + {COR}}{1 + \left( {m/M} \right)}}} & \lbrack 1\rbrack\end{matrix}$

-   -   where v is the velocity of the ball immediately after impact, U        is the velocity of the club head immediately before impact, m is        the mass of the ball, M is the mass of the club head, and COR is        the coefficient of restitution of the ball.

The COR of a golf ball is determined empirically. The ball is launchedat a predetermined velocity (v_((initial))) toward a flat rigid object,such as a large steel plate fixed to a wall, and the velocity ismeasured after the ball bounces off of the plate (v_((final))) in amanner such that the impact is perpendicular to the plate. The COR iscalculated as shown in equation 2:

COR=v _((final)) /v _((initial))  [2]

Basically, COR determines the elasticity of a golf ball and the valuelies between an ideal case where all the energy at impact is returned tothe ball and the final velocity matches the initial velocity, with CORequal to 100% or 1.0 and the case where none of the energy at impact isreturned to the ball and the final velocity is zero (i.e., simply dropsto the floor) and COR equals 0% or 0. The COR of a typical polymericgolf ball is around 70-85%. COR may change over the range of initialvelocities—i.e., COR at an impact velocity of 10 meters per second maybe different than the COR at an impact speed of 50 meters per second.

If the COR of the golf ball for a given collision is high (i.e. near 1.0or 100%), then very little of the kinetic energy is lost during thecollision. However, if the COR in a given collision is low, then morekinetic energy is lost during the collision. This energy loss resultsfrom internal friction between the polymeric molecules as the balldeforms from the spherical shape to an elongated sphere during maximumdeflection, and back to the spherical shape after impact.

It has been observed that in some instances, depending on the materialsused for construction, the COR of golf balls with stiff metal coreshaving a smooth surface or surfaces can be much less than that of atypical golf ball, in some cases ranging as low as 40%.

For COR, the key parameters are the properties of the core, such as thestiffness of the core, and the properties of the mantle layer. Thestiffness may be attributed to either the properties of the materialused to construct the core, such as the hardness, modulus of elasticity,toughness, etc., or properties associated with the shape and size of thesphere, such as the moment of inertia, the section modulus, surfacefeatures, etc. In addition, the properties of the polymers or othermaterials surrounding the sphere, as well as any materials within thesphere are important. The ability to minimize or otherwise reduce lossesupon impact will generally reduce the kinetic energy from the impactthat is lost to heat, thereby increasing the COR of the ball.

Further, it has been observed that some thermoplastic materials, such asDuPont HPF™ materials perform very well in golf balls with a hollowmetal core with respect to durability, but often players complain aboutthe hard feel of these golf balls. It has also been found that someformulations of polybutadiene have excellent performance characteristicsand feel to a golfer, but durability is very poor, with cracks formingin hollow metal core balls after just a few high-speed impacts.

A blend of materials that provides the benefits of both materials aswell as a suitable COR is provided herein.

The present invention therefore generally provides golf balls having anouter cover with a dimpled pattern and a stiff spherical core, whereintermediate layer between the outer cover and the core is made from ablend of a thermoplastic material and a second phase elastomericmaterial that is dispersed within the thermoplastic material to providematerial characteristics that are a combination of the two materials.This material is referred to as a Thermoplastic Elastomer Composite, orTEC.

Referring now to FIG. 1, an improved golf ball according to oneembodiment of the present invention is illustrated in cross section. Thegolf ball 100 includes a hollow metal sphere 110, with internal voidspace 115, surrounded by the Thermoplastic Elastomer Composite layer120, and cover layer 130. The outer surface 140 may include surfacefeatures such as dimples to increase flight characteristics, as is wellknown in the art.

As discussed more thoroughly in the '225, '957, and '925 patents, thehollow metal sphere 110 may be made of titanium, titanium alloys, orsteel, including carbon steel, stainless steel and steel alloys. Thehollow metal sphere 110 has an outside diameter ranging from about 0.50to 1.50 inches (about 1.27 to 3.8 centimeters), and a thickness of about0.02 to 0.16 inches (0.05 to 0.41 centimeters) and more preferably about0.02 to 0.08 inches (0.05 to 0.20 centimeters). Preferred steels includethe 300 series stainless steels, the 400 series stainless steels andalloy steels, and more preferably 301 stainless steel, 302 stainlesssteel, 304 stainless steel, 430 stainless steel, and ***

The cover layer 130 has a cover outer surface and a cover inner surface,which together define a cover thickness, which is about 4 mm, but may beany thickness between about 1 mm and about 6 mm or between about 2 mmand about 5 mm. The cover has a surface dimple pattern and is preferablymade of SURLYN, but may be also be made of an ionomer, urethane, balata,polybutadiene, or other synthetic elastomer, or any other materialsuitable for a golf ball cover, as is known in the art. The cover layeralso forms the golf ball diameter, which is preferably 42.67 mm (1.68inches), to meet USGA and industry standards, but may be any diameterequal to, greater or less than 42.67 mm, preferably between about 40 mmand about 45 mm.

The hollow metal core 110 has an outer diameter and is preferably about22.86 mm (0.90 inches) or less to comply with new rules issued by theUnited States Golf Association (USGA) but the diameter may be anydiameter from about 10 mm (0.39 inches) to about 38 mm (1.50 inches), orfrom about 25.4 mm (1.0 inches) to about 35.6 mm (1.4 inches). The outercore surface and the inner core surface together define a corethickness, which is preferably about 1.82 mm, however the core thicknessmay range from about 0.5 mm to about 6.4 mm.

Referring now to FIG. 2, an improved golf ball according to anotherembodiment of the present invention is illustrated in cross section. Thegolf ball 200 includes a solid spherical core 210, surrounded by aThermoplastic Elastomer Composite layer 220, and cover layer 230. Theouter surface 240 may include surface features such as dimples toincrease flight characteristics, as is well known in the art.

The spherical core 210 may be made of various materials and ispreferably designed to have high stiffness. One set of materials thatcan be used to create high stiffness cores is a blend of polymer-ceramiccomposites, as described in more detail in the related pending U.S.patent application Ser. No. ______ Many polymers and ceramics may beused for this type of composite. Injection molding polymers for the corecomposites include, but are not limited to nylon, polyethylene, andpolystyrene, and ABS. Ceramics that can be used as the strengtheningphase in the polymer matrix composite include, but are not limited toSilicon Nitride (Si3N4), Silicon Carbide (SiC), Titanium Diboride(TiB2), Titanium Carbide (TiC), Aluminum Oxide (Al2O3), Zirconium Oxide(ZrO2), and Boron Carbide (B4C). Other materials may be as thestrengthening phase in the polymer matrix composite as well. Forexample, carbon fiber, carbon nanotubes (CNTs), graphene, and otherrecent materials may provide significant stiffening of a polymer orelastomer when used in a composite as described above. Furthermore,elastomers may also be employed as the matrix or mixed with a polymer toprovide the matrix.

Referring now to FIG. 3, an improved golf ball according to anotherembodiment of the present invention is illustrated in cross section. Thegolf ball 300 includes a hollow metal sphere 310, with internal voidspace 315, surrounded by a Thermoplastic Elastomer Composite layer 320.The outer surface 340 may include surface features such as dimples toincrease flight characteristics, as is well known in the art. The outersurface 340 may also be painted with various materials, as is known inthe art.

The Composite Thermoplastic Elastomer (TEC) materials may be used in agolf ball without a separate core. For example, referring now to FIG. 4,an improved golf ball according to another embodiment of the presentinvention is illustrated in cross section. The golf ball 400 iscomprised of Thermoplastic Elastomer Composite 420. The outer surface340 may include surface features such as dimples to increase flightcharacteristics, as is well known in the art. The outer surface 340 mayalso be painted with various materials, as is known in the art.Optionally, this ball may include a separate cover made of SURLYN, butmay be also be made of an ionomer, urethane, balata, polybutadiene, orother synthetic elastomer, or any other material suitable for a golfball cover, as is known in the art.

In addition to the embodiments shown in FIGS. 1 through 4, the presentinvention may be applied toward other multi-piece designs using greaterthan three pieces, e.g., three, four, five, etc. pieces, in whichinstance the hard sphere may serve as an intermediate layer or as aspherical core, hollow or otherwise. Many multi-layer golf balls todayinclude several layers near the cover, to control spin and other playingcharacteristics. The present invention may be employed in these designsas well.

The resulting hollow metal sphere will have a yield strength greaterthan about 350 MPa, more preferably 450 MPa, and more preferably greaterthan about 650 MPa.

Thermoplastic Elastomer Composites

The Thermoplastic Elastomer Composite (TEC) is a multi-component polymerm material, comprised of at least one injection moldable thermoplasticmaterial, also referred to as the injection moldable fraction, and asecond phase material dispersed throughout the injection moldablethermoplastic. Preferably, the second phase material is an elastomericmaterial, but may be any other material that is highly resilient.

In one embodiment, the TEC is comprised of a thermoplastic material andpolybutadiene as the second phase. The thermoplastic material maycomprise one or more polymers from the following group, an ethylene(meth)acrylic acid ionomer (such as HPF™ resin made by DuPont), apolyether block amide (such as Pebax® resin made by Arkema Group),urethane/polyurethane, and/or other commercially availablethermoplastics. The polybutadiene may be blended into the injectionmoldable fraction by adding particles, fragments, and other forms into ablending extruder or mixed with the polymer in the injection molderhopper just prior to injection molding. With this second phase (ormultiple additional phases) material is incorporated into to thethermoplastic to from the TEC that is injection molded, increasing thescrew and backpressure during injection molding may improve dispersionof the material into the polymer.

Optionally, other materials may be added to the two-component mix tofurther enhance material properties. One such material is clay ofvarious sizes, including nanometer sized materials. The nanoclaymaterial may be added in the form of a nanocomposite, i.e. nanoclayparticles contained in a polymer carrier such as polypropylene (such asNanoblend™ Concentrate 1001 made by PolyOne Corporation). The weightpercent of the nanoclay material is determined by including the weightof the clay and any polymer carrier. Between about 0.1% and 10% andpreferably about 0.1% to 5% by weight of a nanoclay material may beadded to the injection moldable fraction.

Nano-materials may also be used to tailor the characteristics of theTEC. Nanomaterials are generally those that exhibit characteristicsbased on controlling the composition of the material at a sub-micrometerlevel, to vary the strength, ductility, hardness, formability, crackpropagation resistance, etc., or a combination thereof. By varying theamount of dispersions within the TEC, the durability, resilience andother properties may be tailored. Thus, nanosize materials, such asmetallic, ceramic, or clay powders, carbon-nanotubes, etc., may be usedas the second phase may not only to carry a portion of the load, but mayalso interact with the matrix material dislocations or grain boundariesto tailor the strength or stiffness.

Between about 1% and 80% and preferably between about 10% and 60% byweight of the Thermoplastic Elastomer Composite is polybutadiene orother dispersed phase.

The TEC allows the golf balls of the present invention to be made usingconventional economical processes and techniques as are presentlyemployed in the art such as injection molding so that the ball will bespherical in shape, have equal aerodynamic properties, and have equalmoments of inertia about any axis through its center.

Multi-Layer Cores and Mantles

The material sets, polymer layers, and processing conditions may betailored to achieve the desired final characteristics. Therefore, thefinal design will generally be the sum of the responses from theindividual layers and any interplay between the layers. The performancemay therefore also be tailored, to some degree, by controlling theinterplay between the layers of a golf ball.

The normal force at impact between a golf ball and a golf club when theaverage golfer strikes the ball can be on the order of 2000 lb. Thus,durability of the materials that comprise a golf ball must be able towithstand this impact force many times while retaining their originalshape following impact and without degradation of the ball's coefficientof restitution. For golf balls with highly stiff cores, achieving a golfball with good energy transfer between layers and sufficient durabilityis a challenge.

For example, it has been observed that the layer or layers surroundingthe core in a golf ball incorporating a highly stiff core, such as ahollow metal core, may fracture upon repeated impact by a golf club atswing speeds that are typical of the average golfer. More specifically,the transfer of useful energy upon impact between the layers may bereduced due to the fracturing or otherwise degradation of materials. Onecontributing factor for this degradation is the large differentialelastic modulus between the separate layers. It would be preferable todesign a golf ball such that the elastic modulus is within two (2)orders of magnitude, of an adjacent layer.

The elastic modulus of the metal is much higher than the typical modulusrange of polymeric materials. It is thus necessary to have a transitionfrom the metal to the polymeric materials such that the modulusdifference between the innermost layer and the hollow metal core is notgreater than two orders of magnitude. Molding materials in several stepsto produce a multi-component ball with several TEC layers, where eachlayer is comprised of a different combination of dispersions and resultsin decreasing stiffness from each layer moving out from the stiff core,is one example of a golf ball that achieves this objective. Theselection for each layer will generally be determined throughexperimental means, testing each layer individually as well asvariations of completed balls.

Optionally, it may be desired to reduce the stiffness of a stiff metalcore to some degree or to increase the stiffness. One method to modifythe stiffness of the hard sphere or of any other layer may be anyfeature that modifies the manner in which the golf ball responds to aforce as compared to the response of the sphere without the feature. Thestiffness of the sphere may be controlled by including at least onegroove or any other indentation in the hard sphere core or layer. Thegroove or grooves serve to locally reduce the wall thickness of thesphere, or reducing the thickness of the layer near the outer surface ofa solid core, thereby reducing the stiffness of the hollow metal spherecore by allowing larger deformations under a given load withoutsignificantly reducing the total mass of the sphere.

One embodiment of the present invention provides a golf ball having ametal or other hard material sphere core or layer surrounded by a mantlelayer and a cover layer, where the sphere core has at least oneindentation or groove. Although the invention is described by way ofhaving vertical or horizontal grooves, it is understood that a similarresult may be achieved with other regularly patterned indentations, suchas with perforations, protrusions, or a combination thereof, that reducethe wall thickness of the hard sphere core at the desired locations anddepth to reduce the stiffness of the core thereby allowing largerdeflections at impact, e.g., elastic deformations, and is also notlimited thereto.

Preferably, the golf balls of the present invention meet thespecifications of the USGA.

EXAMPLES

Examples of golf balls made according to the present invention are shownbelow:

Example 1

Three piece ball: hollow 301 stainless steel core having an elasticmodulus of 193 GigaPascals (GPa) and a thickness of approximately 0.039inches and a diameter of 1.1 inches, surrounded by a polyether blockamide as the transition agent which has an elastic modulus of 290MegaPascals (MPa), and then further surrounded by a layer of polymericresin having an elastic modulus of 86 MPa, and covered with an ionomerwith an elastic modulus of approximately 350 MPa and a thickness of0.063 inches.

Other materials, such as polybutadiene, urethanes, and various resinsmay be used as layers, provided the constraint is met that no twoadjacent layers have no more than two orders of magnitude difference intheir respective elastic modulus.

Example 2

Three piece ball: hollow metal core, second polymer layer comprising aDuPont HPF 1000 or HPF 2000 resin blended with 0.25-1.0 mm particulatepolybutadiene and a Surlyn cover. The hollow sphere comprising a 301stainless steel core with an inside diameter of 21.21 mm (0.835 inches)and an outside diameter of 22.86 mm (0.9 inches), the specific gravityof the stainless steel of 7.8 and a core mass of 10.125 grams. HPF resin(base resin specific gravity=0.96) with a layer thickness of 8.32 mm(0.3275) inches blended with 25% polybutadiene in particulate form witha size of 0.25-1.0 mm, and 1% by weight of nanoclay material in apolypropylene carrier (such as PolyOne® Nanoblend™ Concentrate1001—specific gravity of about 1.1) with a total layer mass of 27.4grams. Further comprising a SURLYN (specific gravity of about 0.95)cover of thickness 1.59 mm (0.0625 inches), and a mass of 7.95 grams.The pressure of the residual gas or air in the hollow metal sphere isless than about 1 mbar above atmospheric pressure. The total mass of theball is 45.5 grams.

As described above, the improved golf ball of the present inventionprovides improved performance characteristics including high accuracy,minimization of hook and slice when improperly hit, long distance, andbite without adversely affecting rebound characteristics. The design ofthe golf ball allows variations in the material and the size of thecore, mantle layer(s), and outer cover or multiple cover layers in orderto optimize performance characteristics.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

In the drawings and specification there has been set forth preferredembodiments of the invention and although specific terms are employed,the terms are used in a generic and descriptive sense only and not forthe purpose of limiting the scope of the invention being set forth inthe claims.

1. A golf ball comprising: a cover layer having an outer surfacedefining a dimpled pattern and an inner surface defining with the outersurface a cover thickness; and a stiff sphere core disposed within thecover layer, wherein the hard sphere has a stiffness of at least 1 GPa;and a mantle layer having an inner surface mating with the outer surfaceof the spherical core and a outer surface mating with the inside surfaceof the cover layer, comprised of a mixture of a thermoplastic andelastomer.
 2. A golf ball according to claim 1, wherein the hardspherical core is made of a hollow metal core.
 3. A golf ball accordingto claim 1, wherein the mantle layer is comprised of a mixture of athermoplastic and elastomer, wherein the elastomer is in particulateform.
 4. A golf ball according to claim 3, wherein the mantle layer iscomprised of a mixture of a thermoplastic and elastomer, wherein theelastomer is in particulate form.
 5. A golf ball according to claim 4,wherein the mantle layer is comprised of a mixture of a thermoplasticand elastomer, wherein the elastomer is in particulate form and has amass fraction of less than 60%.